This form definition
$form->addRadioList('test', 'Test', [
'1' => "one",
'2' => "two",
]);
$form->setDefaults(['test' => '1']);
with following rendering
{foreach ['1', '2'] as $key}
{input test:$key}
{label test:$key /}
{/foreach}
will not check the default radiolist value due to strict comparison here. Maybe the $key might be fixed by the same trick as used here. What do you think?
Example is quite artificial, but when the arrays are generated somewhere, it is not so obvious what is happening...